1. Field of the Invention
The present invention relates to a pressure limiting valve, in particular for arrangement in a return pipe of a common-rail system of an internal combustion engine with a valve housing, which features a housing head and a hollow cylindrical housing jacket in which there is an axial inlet opening and at least one radial outlet opening axially separated from the inlet opening in a valve base of the valve housing, whereby an inner valve seat for a valve body connects in the valve base to the inlet opening, and whereby an axially mobile valve piston is arranged between the valve body and a closing spring, which produces a closing force against the pressure acting at the inlet opening.
2. Related Technology
Such pressure limiting valves are used in fuel return pipes of so-called common-rail injection systems of internal combustion engines. In common-rail fuel injection—also called accumulator injection—a high-pressure pump raises the fuel to a high pressure level. The pressurized fuel fills a pipe system, the accumulator, which is continuously under pressure during engine operation. The system features a joint pressure pipe, the so-called rail, for several injectors. Fuel is delivered via the pressure pipe at high pressure, and injected via the injectors in doses into the internal combustion engine. The power of the high-pressure pipe is hereby arranged such that at any time and in any operating state, more fuel can be delivered than the engine requires. The fuel that is not injected is in each instance returned via the return pipe to a section pipe of the fuel pump or to the tank. Here it is generally necessary to maintain a specific minimum pressure within a range of up to approximately 10 bar in the low-pressure range of the injectors. For this purpose, a pressure limiting valve of the described type, which is frequently also called a pressure retention valve, as is known in similar form from DE 43 11 856 A1, can be mounted in the return. This valve fulfills the described tasks of maintaining the pressure of the fuel at a defined value, or more specifically limiting it to this defined value.
In practical use, it has been demonstrated, in particular for a valve with a spherical valve element, as described in DE 43 11 856 A1, that under specific operating conditions, there may be damage to or even total failure of the pressure limiting valve.
It is the purpose of this invention to improve a pressure limiting valve of the described, generic type with regard to operating safety, and thus avoid damage or even total failure.